The present invention relates to power devices, and in particular high voltage diodes, transistors, power MOSFETs, IGBTs, thyristors, MCTs, and the like (“power devices”).
High voltage power devices are fabricated by semiconductor processing techniques on a single crystalline semiconductor substrate, such as a silicon wafer. Conventional semiconductor processing techniques include doping and implanting, lithography, diffusion, chemical vapor deposition (CVD), wet and dry etching, sputtering, epitaxy, and oxidizing. A complex sequence of these processing techniques is required to produce the conventional power devices having a high breakdown voltage.
In conventional power devices, e.g., thyristors and diodes, an aluminum (Al), separation diffusion process is used to connect the backside of a die of to the top surface of the die. These vertical separation diffusion structures are referred to as “pipes” or “sinkers.” Electrically it connects the potential of the back surface to the top surface areas of the die whereon the aluminum diffusion regions are defined. By using this technique it is possible to define the potential of these regions. For example, this technique makes it possible to obtain high breakdown voltages for the devices, especially in a planar manufacturing method. These aluminum diffusion regions are preferably located at the edges of the die to provide a given potential condition at these scribe regions whereon dicing would be performed.
These aluminum diffusion regions are formed by making patterned aluminum structures on both sides of the wafer or substrate for use as diffusion sources in a high temperature diffusion process. The two diffusion fronts or regions (from top and backside) meet each other approximately in the middle of the wafer thickness. This merged aluminum region generally has a relatively high resistance due to the low aluminum concentration at its center.